Fluorimetric determination of menadione sodium bisulphite (vitamin K3) in animal feed and premixes by high-performance liquid chromatography with post-column derivatization.

A high-performance liquid chromatographic (HPLC) method for the determination of menadione sodium bisulphite (vitamin K3) in animal feed and premixes is described. After aqueous extraction, the vitamin is converted into menadione, which is extracted and separated on a reversed-phase HPLC column. After menadione has been reduced in a post-column reaction coil, fluorimetric measurement of the reduced vitamin permits the determination of menadione sodium bisulphite in animal feed and premixes at concentrations as low as 0.02 microgram/g. Several types of animal feed have been analysed according to the method described and also with the European Community colorimetric method. From high concentration levels down to ca. 15 micrograms/g the results obtained with the two methods are in good agreement. For concentrations in the range 1-3 micrograms/g (complete diets) a tendency to lower results by the HPLC method is observed. The detection limit of the HPLC method is considerably lower than that of the European Community colorimetric method. The within-assay coefficient of variation of the method applied to feeds is 6.0%. The within-assay analytical recovery of menadione sodium bisulphite added to feeds is 94.4 +/- 6.8% (mean +/- S.D.).